The present invention relates to a process and to equipment for pickling a metal strip, in particular a rolled strip, by means of a pickling plant, through which the metal strip passes and in which the metal strip is pickled using a pickling liquid, the pickling result being a function of pickling parameters.
In order to clean metal strips, in particular in order to remove scale layers on rolled strips, the metal strips are pickled in a pickling plant using a pickling liquid, generally acid. The amount removed by the pickling is a function of pickling parameters. These are, for example: temperature of the pickling liquid, speed at which the metal strip passes through the pickling plant, the acid content in the pickling liquid, the metal content in the pickling liquid, in particular the iron content in the pickling liquid, strip parameters, such as material and geometric dimensions, and the turbulent pressure of the pickling liquid. These pickling parameters have to be set in such a way that as far as possible, the desired amount of material is removed from the metal strip. Deviations from the desired optimum value are associated with high costs. If too much material is removed, i.e., if it is not only the scale layer that is removed from a rolled strip but also metal from the surface of the rolled strip, then the metal or iron content in the pickling liquid is increased to a disproportionate extent. Since the purification of the pickling liquid is complicated and expensive, too high a removal rate is undesirable. In addition, in the event of too high a removal rate, damage to the metal strip may occur. On the other hand, if too much material, in particular too much scale, remains on the metal strip, then this has to pass through the pickling plant again. This additional operation is complicated and expensive.
Setting the pickling parameters to achieve the best possible pickling result is conventionally carried out, by an operator of the pickling plant. However, this leads to fluctuations in the pickling result. The pickling result is to be understood, for example, as the amount of material removed or the amount of scale that has remained on the metal strip.
An object of the present invention is to provide a process and equipment for pickling a metal strip by means of which the pickling result is improved. Furthermore, it is desirable to reduce the costs for the pickling of a metal strip.
According to the present invention, the pickling result is measured and at least one pickling parameter is automatically varied, as a function of the measurement of the pickling result, so as to improve the pickling result. The automatic variation allows the setting of the corresponding pickling parameter by an operator to be dispensed with. In this way, a more constant and better pickling result is achieved. A saving is also made in corresponding operating personnel. The pickling parameters to be set include, for example, the temperature of the pickling liquid in the pickling plant, which is determined, for example, from the temperature of the pickling liquid in the feed into the pickling plant and the temperature of the pickling liquid in the discharge from the pickling plant, the speed of the metal strip, the acid parameters of the pickling liquid, the iron concentration in the pickling liquid, the turbulent pressure of the pickling liquid in the pickling plant and the properties of the metal strip, such as its material and its geometric dimensions. In this case, the temperature of the pickling liquid is the pickling parameter that is particularly suitable for automatic setting. Since the temperature of the pickling liquid in the pickling plant is difficult to measure and difficult to control, use is advantageously made of the feed temperature of the pickling liquid into the pickling plant, the discharge temperature of the pickling liquid from the pickling plant or both temperatures instead of the temperature of the pickling liquid in the pickling plant.
The pickling result is advantageously measured by measuring defects and/or unpickled points on the metal strip. The defects and/or unpickled points are advantageously classified and counted. The classification of the defects and/or unpickled points is in this case advantageously carried out in relation to their size and/or their shape. The defects and/or unpickled points classified and counted in this way are advantageously evaluated. The evaluation is carried out using a fuzzy evaluator, a neural network or evaluator a neural fuzzy assessor. However, the measured values can also be evaluated directly, that is to say unclassified, by a fuzzy evaluated, a neural network or a neural fuzzy evaluated, but indirect evaluation, that is to say the evaluation of the classified and counted defects and/or unpickled points, is more advantageous. The result of the evaluation using a fuzzy evaluator, a neural network or a neural fuzzy evaluator are set points for at least one pickling parameter.